Patients with cystic fibrosis, (CF) suffer from chronic airway infections with the opportunistic pathogen Pseudomonas aeruginosa (PA), and experience worsening, irreversible lung injury leading to premature death. This injury is mediated by an inflammatory process that results, at least in part, from stimulation of the innate immune system by PA lipid A, the bioactive component of lipopolysaccharide (IPS). PA isolates from CF patients constitutively synthesize lipid A with unique structural modifications. The synthesis of these structures may be essential for CF lung disease pathogenesis. PA with unique lipid A could contribute to CF lung disease in two ways: by increasing host inflammatory responses, and by increasing bacterial resistance to elements of host innate immunity, such as cationic antimicrobial peptides (CAMPs) or antibiotics. We therefore propose to identify the relevance and regulation of these lipid A structural modifications to CF pulmonary disease by identifying genes involved in their synthesis, constructing isogenic PA mutant strains unable to synthesize specific lipid A structures, and testing PA with these specific lipid A structures in models of lung inflammation and their susceptibility to CAMPs. These studies will provide insight into bacterial mechanisms that contribute to CF lung disease, including the role of lipid A modifying enzymes. Such enzymes may provide novel targets for the development of drugs to treat PA lung infections and their inflammatory consequences. The focus of this proposal is to further define enzymes required for the synthesis and regulation of cystic fibrosis-specific lipid A, the bioactive component of lipopolysaccharide in a variety of Pseudomonas aeruginosa clinical isolate backgrounds. P. aeruginosa isolates from patients with cystic fibrosis constitutively synthesize lipid A with unique structural modifications. In addition, the role of specific lipid A structures in modulation of the host the innate immune system and inflammatory responses will be determined. These studies could lead to the identification of candidate protein targets that block the synthesis of CF-specific lipid A structures and render P. aeruginosa more susceptible to host cell killing and/or conventional antibiotic intervention.